Roads on Tuesday were closed and posters of Lebanese President Emile Lahud and his Syrian counterpart Bashar al-Assad put up around Beirut ahead of the protest, dubbed the March of a Million by organisers and expected to draw tens of thousands of people.
The demonstration was organised after an unauthorised march led by opposition groups earlier in November, in which hundreds of mainly Christian students called for an end to Syrian interference in its small neighbour.
Syria has roughly 14,000 troops in Lebanon and a major say in Beirut politics. Opposition to Damascus' role in Lebanon has become more vocal in recent months, encouraged by a UN Security Council resolution instructing Syria to pull out.
The US and French-backed resolution in early September aimed to head off the extension of the pro-Syrian Lahud's term through a widely opposed constitutional amendment that was passed regardless shortly afterwards.
Lahud and the government say Syrian involvement in Lebanon is an internal Lebanese matter. Damascus, too, says UN resolution 1559 was prompted by a US desire to put pressure on Syria, not out of concern for Lebanese sovereignty.
Protesters said other countries
had no right to interfere
"We want Syria to stay, we are nothing without Syria," said Ghiwa Ghiyah, a 17-year-old student.
"The United States, France or the United Nations have no right to come and interfere in internal Lebanese affairs," said Ahmad Barini, a 23-year-old student bussed in from north Lebanon for the march. "The issue of the Syrian presence is between Syria and Lebanon."
Syrian-backed Hizb Allah, which has strong support in Lebanon for fighting Israel, joined other pro-Syrian groups in urging followers to turn out for the protest, running appeals to join in on the al-Manar television channel it runs.
Opposition politicians say the attempt to mobilise support risks needless confrontation with the United Nations and threatens Lebanon's cohesion, fragile since the 1975-1990 civil war.